[FFmpeg-devel] [PATCH 4/4] Make the crop filter accept parametric expressions.

[Michael Niedermayer]

On Sat, Sep 11, 2010 at 11:35:58AM +0200, Stefano Sabatini wrote:
> On date Friday 2010-09-10 23:13:45 +0200, Michael Niedermayer encoded:
> > On Fri, Sep 10, 2010 at 06:33:36PM +0200, Stefano Sabatini wrote:
> > [...]
> > > > also i think the values should be cliped into sane integer range and maybe a
> > > > NAN check is needed to
> > > 
> > > The clipping is already performed, and NAN check added.
> > 
> > no its not, you dont clip the double before converting to int
> > and if iam not mistaken C doesnt gurantee not representable types for that
> > not just crashing your program
> 
> Check attached and tell me if you like it.
[...]
> +# trembling effect
> +crop='10+10*sin(n/10):20+20*sin(n/5):w-2*x:h-2*y
> +
> +# erratic camera effect depending on timestamp
> +crop='20+20*sin(3*t):10+10*sin(2*t):w-2*x:h-2*y'
> +
> +# set x depending on the value of y
> +crop='y:10+10*sin(n/10):w-2*x:h-2*y'
> + at end example

if x and y change per frame but w/h cannot then this looks odd

[...]
>  static int config_input(AVFilterLink *link)
>  {
>      AVFilterContext *ctx = link->dst;
>      CropContext *crop = ctx->priv;
>      const AVPixFmtDescriptor *pix_desc = &av_pix_fmt_descriptors[link->format];
> +    int ret;
> +    const char *expr;
> +    double res;
> +
> +    crop->var_values[E  ]   = M_E;
> +    crop->var_values[PHI]   = M_PHI;
> +    crop->var_values[PI ]   = M_PI;
> +    crop->var_values[X  ]   = NAN;
> +    crop->var_values[Y  ]   = NAN;
> +    crop->var_values[W  ]   = ctx->inputs[0]->w;
> +    crop->var_values[H  ]   = ctx->inputs[0]->h;
> +    crop->var_values[N  ]   = 0;
>  
>      av_image_fill_max_pixsteps(crop->max_step, NULL, pix_desc);
>      crop->hsub = av_pix_fmt_descriptors[link->format].log2_chroma_w;
>      crop->vsub = av_pix_fmt_descriptors[link->format].log2_chroma_h;
>  
> -    if (crop->w == 0)
> -        crop->w = link->w - crop->x;
> -    if (crop->h == 0)
> -        crop->h = link->h - crop->y;
> +    if ((ret = av_parse_expr(&crop->x_pexpr, crop->x_expr, var_names,
> +                             NULL, NULL, NULL, NULL, 0, ctx)) < 0 ||
> +        (ret = av_parse_expr(&crop->y_pexpr, crop->y_expr, var_names,
> +                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> +        return AVERROR(EINVAL);
> +
> +    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
> +    crop->var_values[Y] = av_eval_expr(crop->y_pexpr, crop->var_values, NULL);
> +    /* evaluate again x as it may depend on y */
> +    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
>  
> +    if (normalize_double(&crop->x, crop->var_values[X]) < 0 ||
> +        normalize_double(&crop->y, crop->var_values[Y]) < 0) {
> +        av_log(ctx, AV_LOG_ERROR,
> +               "Too big value or invalid expression for x or y. "
> +               "Maybe the expression for x:'%s' or for y:'%s' is self-referencing.\n",
> +               crop->x_expr, crop->y_expr);
> +        return AVERROR(EINVAL);

this could trigger for unknown pos/ts


[...]
> +    /* FIXME: when the TB will be settable */
> +    crop->var_values[T]   = (double)picref->pts / AV_TIME_BASE;

AV_NOPTS_VALUE

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
it to them? Then do not be too eager to deal out death in judgement. For
even the very wise cannot see all ends. -- Gandalf
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